I need help on fail inspection on my 95' Chevy Sub. V8 5.7Lt First time fail on HC(PPM) and NOx(ppm) and I have change all spark-plug and wire, Distributor cab and rotor, and the EGR valve and take back to inspection again (second time) the HC(PPM) is still FAIL **The NOx(ppm) is pass now** What should go wrong?

Thank you

 

cat plugged?

 

What is cat plugged?

 

suggesting the catalytic converter is plugged

 

try replacing O2 sensors, catalytic converter are rarely ever plugged. If O2 sensors are bad, you will fail inspection

 

a clogged catylic converter is a fairly common condition. It's not rare at all.

 

on an older burban, I would htink there is a good chance the cat is plugged....just throwing it out there, I dont have emmissions here Thank god, so no idea what they even check for...

 

1995? Do you have the OBDII computer?
Here's a couple ideas...

Just go to Autozone or somplace like that (Pep Boys?) and have them do a free scan of the computer for codes. Even if the check engine light is not on, there may be out-of range MIL codes that indicate where the bad parts are. A free scan beats guessing what's bad.
If no codes, try this:
For high HC, check for dirty air filter, bad fuel filter, bad fuel pressure regulator, etc. Could also be a bad injector or injector harness wire - if multiport. Also, if you're borderline on the HC reading, change your oil. That will cut HCs by 20 - 50 ppm.
You didn't say if the motor runs rough. That would be important to know. You're sending too rich of a mixture out the pipe.

One last trick, run you truck down to almost empty. Then put just a couple gallons of regular plus a few bottles of Heet gasline antifreeze or acetone (if you can get it). Your truck won't run its best, but you'll be throwing less HC per per RPM while testing. Alcohol just has less energy (HC) than gas. After the test, fill with good stuff.

Good luck stickin' it to the [emissions] man

 

How many miles on the truck? If you changed everything even the PCV valve I would get gumout fuel injector cleaner the spray can. You might also have carbon build up in the heads which would require removing them and cleaning.